481 research outputs found
Nonstationary Stochastic Resonance in a Single Neuron-Like System
Stochastic resonance holds much promise for the detection of weak signals in
the presence of relatively loud noise. Following the discovery of nondynamical
and of aperiodic stochastic resonance, it was recently shown that the
phenomenon can manifest itself even in the presence of nonstationary signals.
This was found in a composite system of differentiated trigger mechanisms
mounted in parallel, which suggests that it could be realized in some
elementary neural networks or nonlinear electronic circuits. Here, we find that
even an individual trigger system may be able to detect weak nonstationary
signals using stochastic resonance. The very simple modification to the trigger
mechanism that makes this possible is reminiscent of some aspects of actual
neuron physics. Stochastic resonance may thus become relevant to more types of
biological or electronic systems injected with an ever broader class of
realistic signals.Comment: Plain Latex, 7 figure
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Comparison of Microstructures and Mechanical Properties for Solid Cobalt-Base Alloy Components and Biomedical Implant Prototypes Fabricated by Electron Beam Melting
The microstructures and mechanical behavior of simple, as-fabricated, solid
geometries (with a density of 8.4 g/cm3), as-fabricated and fabricated and annealed
femoral (knee) prototypes all produced by additive manufacturing (AM) using electron
beam melting (EBM) of Co-26Cr-6Mo-0.2C powder are examined and compared in this
study. Microstructures and microstructural issues are examined by optical metallography,
SEM, TEM, EDS, and XRD while mechanical properties included selective specimen
tensile testing and Vickers microindentation (HV) and Rockwell C-scale (HRC) hardness
measurements. Orthogonal (X-Y) melt scanning of the electron beam during AM
produced unique, orthogonal and related Cr23C6 carbide (precipitate) cellular arrays with
dimensions of ~2μm in the build plane perpendicular to the build direction, while
connected carbide columns were formed in the vertical plane, parallel to the build
direction.Mechanical Engineerin
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Effect of Build Parameters and Build Geometries on Residual Microstructures and Mechanical Properties of Ti-6Al-4V Components Built by Electron Beam Melting (EBM)
In this study, involving additive manufacturing (AM) using electron beam melting (EBM), we
have examined build defects which result from beam tripping, porosities (including unmelted or
unsintered zones) due to excursions from optimal build parameters (especially variations in melt
scan beam current and scan speed), and gas bubbles trapped in atomized Ti-6Al-4V starting
powder as well as recycled powder, and retained in the build. At optimized build conditions we
have also examined microstructure-mechanical property (hardness, tensile strength, and
elongation) variations for multiple rake building and multiple melt scans using optical
metallography and scanning and transmission electron microscopy (SEM and TEM). These
build variances cause cooling rate variances which promote α-phase growth and variations in
dislocation density, as well as α-to-α' (martensite) phase changes, all of which produce some
degree of mechanical property variations. These features (especially α-to-α' phase changes) are
notable on comparing solid builds in comparison with a variety of mesh arrays where strut
dimension and build-element complexities alter the cooling rates in a significant way. We
illustrate these microstructure variations with corresponding variations in microindentation
hardness measurements made directly on fine mesh (strut) structures. Finally, we have examined
Ti-6Al-4V powder chemistries and solid build chemistries which for single-pass melt scans at
optimized build conditions are shown to be relatively constant up to 40 cycles of powder reuse
with the exception of Al content which was reduced by 10 to 15% in solid builds at optimized
conditions. However, Al loss in solid builds approached 25% for multiple (2 and 3) melt scans,
while no changes in Ar gas-bubble density were observed with changes in α-phase (grain) width
which increased from 3 µm for a single melt scan to 4.5 and 6 µm for 2 and 3 melt scans,
respectively. Corresponding Rockwell C-scale (HRC) hardness varied from 37, 36, and 35,
respectively; with ultimate tensile strengths exceeding 1.2 GPa at elongations of 12% or higher
for this melt scan sequence.Mechanical Engineerin
kt Effects in Direct-Photon Production
We discuss the phenomenology of initial-state parton-kt broadening in
direct-photon production and related processes in hadron collisions. After a
brief summary of the theoretical basis for a Gaussian-smearing approach, we
present a systematic study of recent results on fixed-target and collider
direct-photon production, using complementary data on diphoton and pion
production to provide empirical guidance on the required amount of kt
broadening. This approach provides a consistent description of the observed
pattern of deviation of next-to-leading order QCD calculations relative to the
direct-photon data, and accounts for the shape and normalization difference
between fixed-order perturbative calculations and the data. We also discuss the
uncertainties in this phenomenological approach, the implications of these
results on the extraction of the gluon distribution of the nucleon, and the
comparison of our findings to recent related work.Comment: LaTeX, uses revtex and epsf, 37 pages, 15 figure
Factorization Breaking in Dijet Photoproduction with a Leading Neutron
The production of dijets with a leading neutron in ep-interactions at HERA is
calculated in leading order and next-to-leading order of perturbative QCD using
a pion-exchange model. Differential cross sections for deep-inelastic
scattering (DIS) and photoproduction are presented as a function of several
kinematic variables. By comparing the theoretical predictions for DIS dijets to
recent H1 data, the pion flux factor together with the parton distribution
functions of the pion is determined. The dijet cross sections in
photoproduction show factorization breaking if compared to the H1
photoproduction data. The suppression factor is S = 0.48 (0.64) for resolved
(global) suppression.Comment: 16 pages, 5 figure
Temporal changes in tau phosphorylation and related kinase and phosphatases following two models of traumatic brain injury
Published: November 09, 2018A history of traumatic brain injury (TBI) is linked to later neurodegeneration, with a key feature accumulation of hyperphosphorylated tau. Tau is a microtubule stability protein that undergoes frequent cycles of phosphorylation and dephosphorylation due to kinases and phosphatase activity. Hyperphosphorylation of tau destabilizes microtubules interrupting axonal transport, as well as promotes aggregation disturbing synaptic dysfunction. Aberrant phosphorylation of tau post-injury is thought to be a key player in later neurodegeneration. However, it is not known whether type of TBI- a single severe injury compared to repeated mild injuries- affects the time course of tau accumulation or the pattern of changes in kinases and phosphatases that facilitate this phosphorylation. To investigate, male Sprague Dawley rats were subjected to either a single moderate/severe or 3 mild TBIs spaced 5 days apart (rmTBI) utlising the Marmarou impact-acceleration model. Levels of cortical ptau (AT180, pSer422, oligomeric tau), pGSK3β, pCDK5, pERK1/2, pAkt and PP2Ac were evaluated at 24h, 7 days, 1 month and 3 months post-injury, with changes in tau phosphorylation confirmed via immunohistochemistry. A similar time course of AT180 tau phosphorylation was seen irrespective of the nature of the initiating insult, with a spike at 24h post-injury return to baseline and then increasing chronically at 3 months post-injury. In line with this, levels of PP2Ac were decreased at 24h and 3 months post-injury, indicating a potential loss of phosphatase activity. Interestingly, minimal changes were seen in the kinases examined, with a spike in phosphorylation of GSK3β, at the
inhibitory Ser site, at 24h and 3 months following rmTBI, but not single moderate severe TBI, suggesting a possible protective effect only post-rmTBI. This study highlights that changes in levels of phosphorylated tau are similar, regardless of the initiating injury, and highlights the need to further understand the driving mechanisms behind this phenomenon.Lyndsey Collins-Praino, Daniel Gutschmidt, Jessica Sharkey, Alina Arulsamy, and Frances Corriga
Influencia del agua en la esterificación enzimática de ketoprofeno racémico con etanol sin co-solvente agregado
Las lipasas son las enzimas más comúnmente usadas para producir dexketoprofeno mediante resolución cinética. Este isómero es farmacológicamente activo, por lo que su obtención de forma pura disminuiría los efectos adversos del AINE
Single-Inclusive Jet Production in Polarized pp Collisions at O(alpha_s^3)
We present a next-to-leading order QCD calculation for single-inclusive
high-p_T jet production in longitudinally polarized pp collisions within the
``small-cone'' approximation. The fully analytical expressions obtained for the
underlying partonic hard-scattering cross sections greatly facilitate the
analysis of upcoming BNL-RHIC data on the double-spin asymmetry A_{LL}^{jet}
for this process in terms of the unknown polarization of gluons in the nucleon.
We simultaneously rederive the corresponding QCD corrections to unpolarized
scattering and confirm the results existing in the literature. We also
numerically compare to results obtained with Monte-Carlo methods and assess the
range of validity of the ``small-cone'' approximation for the kinematics
relevant at BNL-RHIC.Comment: 23 pages, 8 eps-figure
Next-to-leading order QCD corrections to A_TT for prompt photon production
We present a next-to-leading order QCD calculation of the cross section for
isolated large-p_T prompt photon production in collisions of transversely
polarized protons. We devise a simple method of dealing with the phase space
integrals in dimensional regularization in the presence of the cos(2 phi)
azimuthal-angular dependence occurring for transverse polarization. Our results
allow to calculate the double-spin asymmetry A_TT for this process at
next-to-leading order accuracy, which may be used at BNL-RHIC to measure the
transversity parton distributions of the proton.Comment: 19 pages, LaTeX, 2 figures as eps file
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